Dolly the Sheep Has Four Clones, and They're Aging Normally

Two decades ago, the first-ever animal to be cloned from an adult cell, Dolly the sheep was born (July 5 would have been her 20th birthday). Dolly famously died somewhat prematurely, at only six-and-a-half years, which has led to widespread ethical concerns about the potential ill health and/or premature aging of genetic clones. Now, four clones of Dolly have reached nine years old, and according to a new study, they are perfectly normal and healthy.

In 1996, Dolly was cloned using somatic cell nuclear transfer, in which the nucleus from an adult cell is transferred into an egg cell that has had its nucleus removed. She was euthanized at six years old after developing a progressive lung disease, although it was unclear whether the condition was related to her being a clone. On the one hand, her lifespan was significantly shorter than the lifespan of the average sheep, which is typically 10-12 years, and researchers theorized that her telomeres may have been degraded, leading to premature aging. However, she's only a sample of one, and her lung disease is fairly common among sheep, especially ones that are kept indoors.

Then, relatively recently, four more identical clones were made from Dolly's DNA, and now they've all reached the age of nine without any serious health problems. According to the research, published in Nature, they are "as healthy as normal aged sheep."

"Our study demonstrates that a subset of cloned embryos are capable of undergoing successful reprogramming and implantation in the uterus following transfer to surrogates," study leader Kevin Sinclair told Research Gate. "These embryos give rise to viable offspring that age normally."

The study, which the researchers are calling "the first to assess the long-term health outcomes of SCNT in large animals," surveyed not only the Dolly clones, but eight other cloned sheep, and compared them to 5-6-year-old normally aged sheep. Even though the Dolly clones are significantly older, they showed no increased signs of diabetes or joint disease, aside from some cases of mild osteoarthritis, and had normal blood sugar and blood pressure. Overall, it is still somewhat inefficient to clone animals, and the process often fails in the early stages, but once the process succeeds, the animals seem to be exactly the same as a non-cloned animal.

"Our detailed study and less detailed studies by others suggest that once cloned animals get past the first month or two of life they are healthy. However, early pregnancy loss and neonatal losses are still greater with cloning than natural conception or assisted reproduction (IVF). Current research endeavors are attempting to overcome this problem."

The research should still proceed with caution, of course, since there are immediate concerns of unforeseen and inhumane health effects, as well as overarching concerns about the potential dehumanizing implications of human cloning (at one point, Sinclair referred to the sheep's deaths in order to run more complete tests on their organs as "humane experimental endpoint," which sounds straight-up dystopian). But all signs point to cloning technology becoming viable in the near future, and according to Sinclair, it's already becoming more accepted by society.

"Judging from the media interest surrounding the 20th anniversary of the birth of Dolly I would say [the stigma isn't as high]," Sinclair said when asked about attitudes regarding cloning today versus 20 years ago when Dolly was born. "Many of the fears raised back in the late 1990s regarding cloning have disappeared, and people are becoming increasingly reassured that these technologies can be a force for good and not evil. The fact that we have demonstrated that cloned offspring can live long and healthy lives will hopefully reinforce these views."